The present invention relates generally to spin coating and, more particularly, to a fluid-sealed spin bowl, a spin bowl having an external fluid catch area, an apparatus for spin coating a film over a substrate, and a method for spin coating a film over a substrate.
Spin coating is used to form films over substrates in the fabrication of a variety of devices. For example, in the fabrication of semiconductor devices, films of photoresist materials and low dielectric constant materials (sometimes referred to as xe2x80x9clow k materialsxe2x80x9d) are spin coated over the surface of semiconductor wafers. In a typical spin coating operation in which a photoresist coating is applied over the surface of a wafer, photoresist fluid is applied on the surface of the wafer and the wafer is spun at high speeds in a spin bowl. The centrifugal force caused by the rotation of the wafer causes the photoresist fluid to spread over the surface of the wafer and form a film. Excess photoresist fluid that spins off the surface of the wafer drains from the spin bowl through drain holes formed therein and is collected in a stationary drain bowl disposed below the spin bowl.
One problem with conventional spin bowls is that air flows into the bowl through the drain holes as the bowl is spinning. This airflow is caused by the difference between the speed of the air inside the spin bowl and the speed of the air outside of the bowl during spinning. The differing air speeds create a differential pressure that causes air to flow into the spin bowl through the drain holes. Such back flow of air into the spin bowl is undesirable because it adversely affects the characteristics of the film being spin coated on the wafer. For instance, the back flow of air may cause streaks to form on the film or may cause the film to have a nonuniform thickness. Further, the back flow of air may cause premature drying of the film.
In one known spin bowl, the drain holes are straight and extend downwardly away from the wafer. During spinning, these drain holes remain open and allow air to flow back into the spin bowl, and the back flow of air that reaches the film causes the adverse effects described above. In another known spin bowl, a baffle is provided in an effort to minimize the adverse effects of the back flow of air that reaches the film. In this spin bowl, the excess fluid that spins off the surface of the wafer remains inside the bowl during spinning and drains from the bowl when the bowl comes to rest. This approach suffers from two primary drawbacks. First, because the fluid remains in the bowl during spinning, the amount of fluid that can be dispensed before the bowl has to be stopped to drain the fluid therefrom is limited. Second, the fluid captured in the spin bowl can splash onto the wafer during deceleration of the bowl.
In view of the foregoing, there is a need for a spin bowl that prevents air from flowing into the bowl during spinning, but still allows excess fluid to drain from the bowl during spinning.
Broadly speaking, the present invention fills this need by providing a spin bowl that has drain holes configured to trap fluid therein and thereby form a fluid seal that prevents air from flowing into the bowl through the drain holes. An apparatus and method for spin coating a film over a substrate also are described.
In accordance with one aspect of the present invention, a spin bowl is provided. The spin bowl includes a base and a sidewall that extends from the base. The base has an upper portion for supporting a substrate in a horizontal plane and a lower portion that intersects with the sidewall. The lower portion of the base has a plurality of drain holes formed therein proximate to the sidewall. Each of the plurality of drain holes is configured to trap fluid therein during spinning of the spin bowl to thereby form a fluid seal that prevents air from flowing therethrough.
In one embodiment, each of the plurality of drain holes is substantially V-shaped. In another embodiment, the sidewall is configured to define a fluid catch area, and each of the plurality of drain holes is in fluid communication with the fluid catch area. The fluid seal is formed when excess fluid accumulates in the fluid catch area to the point that that the excess fluid blocks either the inlet or the outlet of each drain hole. In this embodiment, each of the drain holes may be oriented so that the inlet is closer to a center of the spin bowl than the outlet. Each of the drain holes is preferably oriented at an angle in a range from about 30 degrees to about 60 degrees relative to the horizontal plane defined by the upper portion of the base. In one preferred embodiment, each of the drain holes is oriented at an angle of about 45 degrees relative to the horizontal plane defined by the upper portion of the base.
In accordance with another aspect of the present invention, an apparatus for spin coating a film over a substrate is provided. The spin coating apparatus includes a rotatable spin bowl and a lid secured thereto so as to define a closed chamber. The rotatable spin bowl includes a plurality of drain holes that are configured to trap fluid therein during spinning of the bowl to thereby form a fluid seal that prevents air from flowing into the bowl through the drain holes in accordance with the present invention. The lid is configured to mate with the sidewall of the rotatable spin bowl so that an underside of the lid is in close proximity to the top surface of the substrate supported on the upper portion of the base.
In accordance with yet another aspect of the present invention, a method for spin coating a film over a substrate is provided. In this method, a substrate is disposed in a spin bowl. The spin bowl is then spun at a relatively low speed. Next, a first fluid is injected into the spin bowl. As the spin bowl is spinning, excess fluid is captured proximate to an outer edge of the spin bowl to form a fluid seal that prevents air from flowing into the spin bowl through drain holes formed in the bowl. Once the fluid seal is formed, a second fluid is applied on the surface of the spinning substrate. The spin bowl is then spun at a relatively high speed to spread the second fluid over the surface of the substrate and form a film. Once the film is formed over the substrate, the spin bowl is brought to rest. After the operation of applying the fluid on the surface of the spinning substrate, the method also may include securing a lid to the spin bowl so that the substrate is enclosed within a closed chamber.
In one embodiment, the first fluid is comprised of a solvent. In one embodiment, the first fluid is injected toward an outer edge of the spin bowl through a backside rinse channel. In one embodiment, the second fluid is selected from the group consisting of a photoresist material, a low k dielectric material, a spin-on-glass, and a dye chemical used in the fabrication of recordable compact discs.
In one embodiment, the excess fluid is captured in substantially V-shaped drain holes. In another embodiment, the excess fluid is captured in a fluid catch area at least partially defined by a sidewall of the spin bowl, and each of the drain holes formed in the bowl is in fluid communication with the fluid catch area. In this latter embodiment, the fluid seal is formed when excess fluid accumulates in the fluid catch area to the point that that the excess fluid blocks either the inlet or the outlet of each drain hole.
In accordance with a still further aspect of the present invention, a spin bowl having an external fluid catch area is provided. This spin bowl includes a base and a sidewall that extends from the base. The base has an upper portion for supporting a substrate in a horizontal plane and a lower portion that intersects with the sidewall. The lower portion of the base has a plurality of drain holes formed therein proximate to the sidewall. The sidewall has an upper portion that extends upwardly from the base and a lower portion that extends downwardly from the base so as to define an external fluid catch area that receives excess fluid that drains from an interior of the spin bowl through the drain holes. The external fluid catch area is configured to retain the excess fluid while the spin bowl is spinning and thereby prevent the excess fluid leaving the bowl at high velocity. In one embodiment, the lower portion of the sidewall is inclined inwardly so that a tip thereof is situated closer to a center of the spin bowl than a point at which the lower portion of the sidewall intersects with the upper portion of the sidewall.
The fluid-sealed spin bowl of the present invention provides a number of significant advantages relative to conventional spin bowls. These advantages include the elimination of streaks caused by the back flow of air into the bowl, improved coat uniformity at all thicknesses, and greater process latitude in the formation of spun films. The primary reason that the fluid-sealed spin bowl affords greater process latitude is that the film can be spun for a longer period of time without drying because of the completely enclosed and scaled environment within the bowl. In the embodiments of the invention in which the excess fluid is trapped in an external fluid catch area, the fluid-sealed spin bowl of the present invention is further advantageous because the use of an external fluid catch area prevents the trapped fluid from splashing onto the wafer, and because its one-piece construction avoids the need for an extra baffle piece as found in one known design. An additional advantage of the external fluid catch area is that it prevents the fluid that drains from the spin bowl during spinning from leaving the bowl and contacting the sidewall of a stationary drain bowl at high velocity. This reduces splashing and atomization of the fluid outside the bowl.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.